Patent GB-749488-A (GB)
Title: Improvements in master-cylinders
IPC: F16J15/16
Filed: 1953-12-31
Abstract: 749,488. Hydraulic master-cylinders. DUNLOP RUBBER CO., Ltd., and TREVASKIS, H. W. Dec. 17, 1954 [Dec. 31, 1953], No. 36286/53. Class 103 (1). A master-cylinder, particularly for use in vehicle braking systems, comprises a stepped cylinder having the smaller diameter end thereof communicating with a mechanism to be operated and the larger diameter end communicating with a liquid reservoir, a piston slidablo in the small diameter end but normally located, when the master cylinder is inoperative, in the larger diameter end and a piston seal, e.g. a washer, abutting the operative face of the piston and adapted to be deflected around an associated domed portion to allow passage of liquid from the larger diameter end to the smaller diameter end when the pressure in the former end is greater than in the latter end. In the embodiment illustrated, the master cylinder comprises a body portion 1 having a cylindrical cavity 2 communicating with a liquid reservoir 4. An end cover 6 is secured to one end of body portion 1 and is provided with an integral sleeve 7 which fits coaxially within the cavity 2; the sleeve 7 having a bore 8 which constitutes the smaller diameter end or the working cylinder of the master cylinder. Slidably and fluid-tightly fitted through a bush 10 fitted in the end of the cavity 2 is a push-rod 11 having a cap 12 fitted to the end of the push-rod projecting exterior of the cavity 2; a helical spring 13 being fitted between the cap 12 and the adjacent end of the body portion 1 and protected from dirt and the like by a cylindrical shield 14 secured to cap 12. The end of the push-rod remote from the cap 12 is provided with a reduced diameter portion 15 on which is fitted a piston 16. When the master cylinder is in the inoperative position (as illustrated) the piston 16 is located in the cavity 2 of the body portion 1 but is a slidable fit in the working cylinder 8. A sealing washer 18, being a slidable fluid-tight fit in the working cylinder 8, is fitted on the reduced portion 15 of the push-rod, abuts a side of the piston 16, and is maintained in position by a locator 19 having a domed portion 22 which is slidable in the working cylinder and acts as a guide for the piston 16. On depression of the cap 12 against spring 13 the piston 16 is forced into working cylinder 8; the increased pressure causing the sealing washer to flatten against the piston 16 to prevent leakage past the periphery thereof. The liquid in the working cylinder 8 and the system communicating therewith, via nozzle 9, is thereby pressurized. On removal of the pressure from the cap 12 the spring 13 moves the piston 16 to its inoperative position shown. If the hydraulic system needs replenishing, the pressure on the working side sure on the working side 18 will be less than the pressure on the other side of the washer due to the static head of liquid in the reservoir. This pressure differential causes the sealing washer 18 to flex against the domed portion of the locator 19 and permit liquid to flow from the reservoir 4 past the periphery of washer 18 to replenish the system.